Conventional magnetorheological (MR) fluid-based devices include MR devices such as an MR damper and an MR clutch. One conventional MR damper includes an MR piston assembly having a ferromagnetic MR piston core, an electric coil, and an outer flux ring. The MR piston assembly is adapted to translate along the central longitudinal axis of the MR damper. The MR piston core has an outer circumferential surface which is substantially coaxially aligned with the central longitudinal axis and which has a circumferential surface slot having a substantially rectangular cross-sectional shape as seen in a transverse cross section of the MR piston core. The electric coil is substantially coaxially aligned with the central longitudinal axis and is disposed in the circumferential surface slot. Some MR piston assemblies include additional electric coils disposed one each in additional circumferential surface slots. The flux ring is concentric with, and spaced outward from, the piston core to form an annular passageway which is located between the flux ring and the MR piston core and which contains MR fluid.
The MR piston assembly of the MR damper also includes a piston rod attached to the MR piston core and first and second MR piston end plates longitudinally surrounding and contacting the MR piston core. The flux ring is attached to the first and second MR piston end plates, and the first and second MR piston end plates each have a through opening in fluid communication with the MR passageway.
One conventional MR clutch includes an MR piston assembly having a ferromagnetic MR piston core and an electric coil. The MR piston assembly is attached to an input shaft or an output shaft of the MR clutch and is adapted to rotate about the central longitudinal axis of the MR clutch. The arrangement of the electric coil and the MR piston core is the same as in the previously-described conventional MR damper.
What is needed is an improved magnetorheological (MR) device having an MR piston assembly.